1. Technical Field
The present invention relates to a semiconductor device, to a liquid crystal device, to an electronic apparatus, and to a method of manufacturing the semiconductor device.
2. Related Art
There has been known a light valve used for a video projector, an image sensor, and an active-matrix liquid crystal display device which use an active-matrix substrate, which is obtained by forming active elements such as thin film semiconductor devices for driving pixels on an insulating substrate made of quartz, glass, or the like.
Projection light is incident on a thin film semiconductor device used in a light valve, however, when the projection light is directly or indirectly incident on a semiconductor film which becomes a channel forming region of the thin film semiconductor device, photo leakage current is generated in the region due to a photoelectric effect. As a result, the characteristics of the thin film semiconductor device are deteriorated. Further, when light is incident on the periphery of a pixel region, there is a possibility that the light is reflected from metal wiring lines or the like, and accordingly, the circuit pattern of the periphery of the pixel region is projected to be displayed.
In order to prevent the above-mentioned problems, JP-A-11-194360 discloses a method of preventing light from being incident on a semiconductor film or a region around the periphery of a pixel by forming a light shielding film between a substrate and a semiconductor film.
However, if the light shielding film is formed on a substrate, a step difference between a surface of the substrate and a surface of the light shielding film is generated as shown in FIG. 6 of JP-A-11-194360. Therefore, when an insulating film and a semiconductor film are laminated thereon, a surface of the insulating film and a surface of the semiconductor film are not flat.
If a thin film semiconductor device is formed by using such a semiconductor film, an element having the step difference in a channel forming region and an element having a flat channel forming region are generated. A semiconductor element having the step difference in the channel forming region is different from a semiconductor element having the flat semiconductor film in the thickness of the semiconductor film, the thickness of the gate insulating film, an electric field effect, etc. Therefore, the electrical characteristics of the semiconductor element having the step difference in the channel forming region is different from those of the semiconductor element having the flat semiconductor film. For this reason, variations of the electrical characteristics occur among a plurality of semiconductor elements formed on the same substrate.
Further, if the semiconductor film is not formed in a flat manner, when the semiconductor film is melted by a thermal process, the material of the semiconductor film flows downward. Thereby, the thickness of the semiconductor film becomes inconsistent, which makes a thinner part of the semiconductor film easily damaged. Further, in the configuration having the step difference, when the light valve or the like is manufactured by using the semiconductor device, there is a possibility that the characteristics, such as the optical transmittance, are degraded.